Oksana Grigorieva is going to court on Monday morning in a bid to have her famed first amendment lawyer Martin Garbus admitted to practice law in California, RadarOnline.com has exclusively learned.

Garbus, the defense attorney in the Pentagon Papers, has been unable to formally represent his client in the bitter custody battle with Hollywood actor Mel Gibson.

PHOTOS: Mel & Oksana In Happier Times

Oprah Winfrey could emerge as a key player in the criminal investigation into Mel Gibson's alleged beating of Oksana Grigorieva.

The Russian musician, 40, filmed a ‘pre-interview’ with the talk-show queen’s producers at her Sherman Oaks, California, home, RadarOnline.com has learned.

PHOTOS: Oksana Grigorieva Has A Mother-Son Movie Date

Los Angeles District Attorney investigators are interested in what Oksana may have said and whether it was consistent with her claims that the Lethal Weapon star punched her twice, while holding their infant daughter Lucia.

Oksana Grigorieva's lawyers have finally snagged a sit-down interview with Mel Gibson, and the all-important deposition will take place next Monday, RadarOnline.com has learned.

But lawyers for the Russian musician are almost certain to hear stone-cold silence when the Lethal Weapon star is grilled about allegations he punched his ex-lover while she held their infant daughter Lucia.

PHOTOS: Oksana Grigorieva Has A Mother-Son Movie Date

Oksana Grigorieva’s legal team is in crisis after her top family law attorney suddenly quit the case before a critical deposition, RadarOnline.com has exclusively learned.

Mitchell Jacobs — a family law attorney who has been a Board Certified Family Law Specialist since 1986 — handed in his resignation on Sunday afternoon, citing frustration with some of the Russian musician’s other legal advisors.

PHOTOS: Oksana Grigorieva Has A Mother-Son Movie Date

It is a brutal blow to Oksana, 40, who is scheduled to be questioned in another deposition on Thursday.

Oksana has claimed her former lover, Oscar winning actor Mel Gibson, punched her in the face while she held their infant daughter Lucia.

Oksana Grigorieva suffered a brutal legal blow when a Los Angeles judge rejected her lead attorney's request to practice law in California, RadarOnline.com has exclusively learned.

Martin Garbus, the famed defense attorney in the Pentagon Papers case, had filed a pro hac vice motion in court Thursday -- a move that would have admitted the New York-based lawyer to practice in the Californian jurisdiction.

"This is devastating for Oksana because here you have her lead counsel unable to work on the case and speak on her behalf in a court of law," said a source.

Oksana Grigorieva FIRED lawyer Sorrell Trope and HIRED high powered Hollywood attorney Lisa Bloom, RadarOnline.com is exclusively reporting.

Speaking to RadarOnline.com, Bloom confirmed the sudden appointment: “Oksana is a brave domestic violence victim and I am honored to assist her in her fight for justice.”

PHOTOS: Oksana Through The Years

As we first revealed, Oksana had previously met Bloom in July, but at the time, she chose not to add the prominent domestic violence campaigner to her team, that is fighting against Oscar winner Mel Gibson.

Oksana has alleged that Mel punched out two of her front teeth, leaving her bloodied, bruised and with a concussion after a brutal fight at his Malibu mansion in January.